PDA

View Full Version : LDR Preamp Single and 3 Input Kit



Light Dependant Resistor
29-09-2013, 16:12
Hi
We have our Light Dependant Resistor Single and 3 Input Kits available at:
http://stores.ebay.com.au/stereo-coffee

We looked at LDR products, and Kits seemed to be missing, certainly there were single input models and others using relays to switch audio outputs, but to our thinking not many strangely were building these to get the best audio from an LDR. We were excited with the wonderful audio LDR's can produce. and filed a patent for the control board as it achieves low voltage between 1.9v and 1.4v with sufficient current, whilst operating as a L pad potentiometer.

We listen carefully with the ESL57's to get the best sound. Before shipping a Kit we then tailor 3 parts on each control board to refine further still.

The kits comprise a assembled Control Board, a assembled LDR Output Board, a Bourns potentiometer, and switch for the 3 input edition. There is NO signal switching, rather the anode of the LDR simply switches on or off, to select or deselect that input. Dorothy and I carefully select NSL32SR2 or NSL32SR2S LDR's to individually match a Series and Shunt pair so you achieve matched pairs of devices. This makes a big difference to stereo balance. Eight LDR's are used for 3 inputs, six for the series and two for the shunt elements.

To get our kits up and running you will need, cable, a 12v regulated power supply, or 12v battery and charger, casework, a few hours, a screwdriver, a soldering iron and ideally a multimeter to check DC polarity. Optional is an additional capacitor for the power supply once polarity is confirmed and if soldering is difficult we can supply a 5mm pitch connector to get you going with 1 input, until soldering gear can be obtained.

Thank you for your support. We look forward to answering any questions you may have.

Chris and Dorothy

Puffin
29-09-2013, 16:46
Interesting product. I made several LDR pre-amps when George released the details some years ago. Some for me and some for other people. The original one I made is still in my system and still going strong. Cost me about £15, plus power supply. These are very underrated IMO.

Good luck with these.

Rob.

Light Dependant Resistor
29-09-2013, 23:55
Hi Rob
Thanks,

We hope the efforts we put into the control circuitry is a step above what occurred a few years ago, without diminishing the prior accomplishments of others.

Yes LDR's are very special when it comes to listening.

Cheers Chris and Dorothy

StanleyB
30-09-2013, 06:28
Good luck with your venture Chris. But be careful when applying for a patent on an application like this.
I myself have considered many patent applications on some of my ideas, but once I had seen what was involved to fight cases I left things as they are.
One major obstacle is when you have to rely on an already patented component from a different company. They can file for a cut of your sales. The Apple/Samsung patent war is a recent example of how messy and expensive things can get.

Light Dependant Resistor
30-09-2013, 08:40
Hi Stanley
Thanks for your advices, patents and their processes are certainly not something i enjoy either.
Cheers / Chris

Light Dependant Resistor
04-10-2013, 07:13
Hi
We have received a number of questions concerning directly wiring to our LDR output board. The advantage we see to not using RCA's is removing another connection point. Our board accommodates generous room for soldering your own wires, so please let us know at checkout if you do not need the RCA block. We will provide a modest refund if the RCA block is not required.

We have received very encouraging feedback on sales so far and with all of our LDR kits we very carefully match the NSL32SR2S , so you get the very best stereo presentation.

Regards / Chris

The Grand Wazoo
04-10-2013, 07:32
Chris,
I hope you don't mind if I make a constructive suggestion?
A common theme that I notice on sales related threads on hi-fi fora is that the person pitching their wares writes the first post while presupposing that the reader has prior knowledge of the item on offer.
I'd think there are an awful lot of people who could make good use of your kit, but don't know it because they haven't got a clue what an LDR is, why it's different from other approaches etc.
Spill the beans on the basics mate! It can only help your cause.

Light Dependant Resistor
04-10-2013, 13:47
Hi
Thanks Chris.

What is a light Dependant Resistor ? and how does it benefit audio reproduction
Imagine a world of audio without switches... Hmm that takes some imagination as switches take many forms. But it is possible when we use a unique device called a Light Dependant Resistor (LDR)

Why are switches bad for audio ? A vast question but easily answered when we start to visualize one contact on another,slipping with different metal types. Up the food chain of switches is the relay, but its still a switch. subject to one contact on another.

An LDR though is quite different on one side a resistor that varies resistance between two leads, and on the other a LED, between the two mediums is just light. We have a device then which has no contacts and acts as a variable resistor. Arranged as a L pad circuit we then have a attenuator that varies with light.

Ideally the LDR should approximate a potentiometer in use, our circuitry achieves this, which greatly assists impedance matching.

Light Dependant Resistor
06-10-2013, 09:06
Here is a build of the 3 input LDR board without the RCA block. Its in a recycled Audio Synthesis PAS02.chassis.
Image shows 3 inputs ,the series LDR pair for the 4th input in this build will be added, I will post another image once this is done.

It shows how the boards can be mounted to suit existing rear plate RCA's with the result of a big improvement to a prior switched attenuator type passive pre amp.

Cheers / Chris

Macca
06-10-2013, 09:42
I've just ordered the single input version, will report in due course.

Light Dependant Resistor
31-10-2013, 07:48
Hi
Stereo Coffee LDR Preamp Kits, http://stores.ebay.com.au/stereo-coffee is early next week releasing a small but important update to our control board. As well as new boards from today onwards ,we will be of course updating for free all of our existing customers with new control boards including shipping cost, ie our customers pay nothing.:)

We invite our customers to contribute to the forum with their thoughts and findings with this update, delivery we anticipate should occur toward end of November.

Regards / Chris and Dorothy

Macca
31-10-2013, 08:08
I'll hopefully be picking up my completed LDR pre-amp from my double E this Saturday so will let you all know my thoughts at some point next week.

r100
07-12-2013, 11:18
Hi Macca, have you had a chance to test the LDR ? I was thinking of getting one myself. Thank's

Macca
07-12-2013, 11:20
No, it is still in the pro shop waiting for them to put it together :(

I'll pop in later and see if he's done it but I doubt it. Typical really they have f**k all to do most of the year and I when I want a job doing suddenly they are overwhelmed with work.

r100
20-01-2014, 19:44
soooo ? any success in getting the job done ? ;-)

Macca
20-01-2014, 19:49
soooo ? any success in getting the job done ? ;-)

Nope. Saw him friday it is still on his to do list. It's a pro shop so they have to put that work first. They have done a few small jobs for me in the past for free so i'm not complaining. I'm still hoping to get it in the next week or two.

r100
20-01-2014, 19:53
Thanks for the feedback. I also got an update from Tortuga Audio recently who will be launching their balanced LDR pre soon. They also offer a DIY kit with two boards, one acting as a "slave board". I'm looking forward to that too as it really looks very promising. Cheers !!

Macca
20-01-2014, 19:55
No probs. I will post up my impressions when I finally get it.

r100
20-01-2014, 20:01
'k thank's

nat8808
19-04-2014, 01:33
Thanks for the feedback. I also got an update from Tortuga Audio recently who will be launching their balanced LDR pre soon. They also offer a DIY kit with two boards, one acting as a "slave board". I'm looking forward to that too as it really looks very promising. Cheers !!

With the right circuit, you can implement a balanced version with just a stereo pair.. It involves blending the hot and cold in order to attenuate the levels on both at the same time.

With a matched quad control, you need to have that quad absolutely perfect else when the balanced signal is converted to single ended at the final stage, you'll have a signal with spurious parts of the signal removed via slight mismatching of the hot and cold attenuation and dependant on volume level too. But hey, I guess that applies to how the balanced signal is made in the first place - really need a transformer or digital 180' phase difference.

lurcher
19-04-2014, 08:50
It involves blending the hot and cold

More like blending the hot and not hot, but I know what you mean :-)

r100
19-04-2014, 12:01
With the right circuit, you can implement a balanced version with just a stereo pair.. It involves blending the hot and cold in order to attenuate the levels on both at the same time.

With a matched quad control, you need to have that quad absolutely perfect else when the balanced signal is converted to single ended at the final stage, you'll have a signal with spurious parts of the signal removed via slight mismatching of the hot and cold attenuation and dependant on volume level too. But hey, I guess that applies to how the balanced signal is made in the first place - really need a transformer or digital 180' phase difference.

i think they (tortuga) got the matching sorted with software.. which imho is the differentiating characteristic of the tortuga vs other LDR pre's... of course the totrtuga is more expensive too

I'm writing this from a phone so please excuse the typos

http://www.tortugaaudio.com/ldr3b-balanced-passive-preamp-update/

Light Dependant Resistor
20-04-2014, 05:25
Hi
A balanced version of our stereo coffee can be done. We have done two of these. We use a double L pad , one pad does Hot, the other does Cold. Matching of 8 LDR's is required for one stereo input as you want hot and cold to be the same. The double L pad configuration requires 2 of our control boards, and a dual gang pot, ... er and many patient hours.

Cheers / Chris

Light Dependant Resistor
09-05-2014, 00:25
Hi
We have reduced our prices on both our 3 input and single input kits http://stores.ebay.com.au/stereo-coffee

Stereo coffee LDR kits do not use relays, rather we provide for our 3 input model, 6 matched Series LDRs and 2 matched Shunt LDR's, To switch inputs we simply turn the anodes of the series pair of LDR's off, the input you were listening fades out to silence and the next commences.

There are very good reasons not to use any switching of signal paths at all, including relays or conventional switches as one contact on another causes audio degradation, and is the very reason why LDR's are used in our kits to overcome any switching of signal paths. We offer our kits with or without the RCA connector block, if you want to direct wire your audio system or choose to use cable of your choice.

Cheers / Chris

Light Dependant Resistor
11-05-2014, 06:18
Hi
A review of our Stereo Coffee LDR 3 input kit :) here: https://lencomotion.wordpress.com/2014/05/07/stereo-coffee-ldr-preamplifier/

Cheers / Chris

Figlet108
11-05-2014, 10:42
Interesting review Chris, and especially relevant here that he compared it to a Khozmo with z-foils.

Light Dependant Resistor
18-05-2014, 22:15
Hi
We have our new website up and running http://www.stereocoffee.com

Cheers / Chris

Light Dependant Resistor
26-06-2014, 09:18
Hi
In response to the unsure present supply to EU markets we have adapted our kit so you get everything less the LDR's. As we all know matching LDR's takes a certain skill set to get resistances close. So this kit is for the more experienced, We will supply you with every bit of assistance. There are many suppliers with overnight or same day delivery of the NSL32SR2S and NSL32SR3 the latter also suitable for this kit.

*** Update, we have now adapted the stand alone kit, with a BIG thanks to NRG Neal's suggestion , so we supply you with matched LDR's which we will have as a separate item available shortly, but with the stand alone you will need to
carefully solder these in. We will do all the matching and labeling ie 1234 for a single input kit and update our instructions with lots of images so you can't make any errors, and you end up with a great sounding kit.***

The stand alone kit is now available at our website http://www.stereocoffee.com and includes in the price an assembled control board, a prepared LDR board for 3 inputs if and when you wish to expand or use them, a 500k potentiometer, and a switch for the anodes.Also flat rate shipping price is included from New Zealand. Separate listing will show matched LDRs as components suiting exact board placement

We will keep you advised when there is clearer indication of our assembled matched LDR provided boards returning to normal supply.

Cheers / Chris

12728

So as we are on the same page the attached schematic shows a diagram of what we first use for getting LDR's close. The diagram shows connection to our control board and to relative points on the LDR board for series and shunt LDR's , so you will need a 250k 1/4 watt and a 56k 1/4 watt resistor, a small breadboard and some wire to attach.

12729

NRG
26-06-2014, 10:11
Chris, I don't see anything stopping you from supplying matched NSL32SR2S and NSL32SR3 separately as 'parts'...

Light Dependant Resistor
26-06-2014, 10:43
Chris, I don't see anything stopping you from supplying matched NSL32SR2S and NSL32SR3 separately as 'parts'...

Thanks Neal, thats a good suggestion !

r100
04-07-2014, 20:12
hi Chris, could you supply a balanced kit with all components including LDR's ( except case and psu) to Switzerland ex EU? price ? thanks

Light Dependant Resistor
05-07-2014, 03:03
Hi Rupert

We have made available our EU markets stand alone kit at http://www.stereocoffee.com full instructions are supplied, as well as our 24/7 customer service help.
With our stand alone kit you will have to place and solder in each LDR to the supplied circuit board. approximate construction time is 3 hours. suggested is a vice for holding the board, a temperature controlled iron and a magnifying lamp.

I will get a letter underway similar to the UK NMO one asking the Swiss ROHS authority if OK to supply built kits, if this much DIY is not what you had in mind.

To achieve a one stereo input balanced kit you will need 2x these stand alone kits, with the pot supplied being a dual, rather than the single pot for unbalanced. We will source a dual gang bourns that is suitable and supply it instead of the single model.

For balanced you will need 8x matched LDRs with each quad matching to the other quad, these being for Hot ( 4x LDR ) and Cold (4xLDR) matched pairs, please allow 3 days for matching of your LDR's
Pairs of LDRs matched ( and understanding with your order you need match of each quad ) are $22.00 each.

So pricing that includes postage will be: $190.00 + $ 88.00 = $278.00 which is USD

We look forward to getting this underway for you.

Cheers / Chris

r100
06-07-2014, 08:45
Hi Chris, thank“s for the breakdown. I will get back to you via your website... cheers

Light Dependant Resistor
25-07-2014, 09:30
Some news:

We are carefully looking at the decisions being made by the European Union as to Cds optocouplers being what now appears as non exempt in draft paper July 2014. However as we observe if parts are available with stockists there appears sensible allowance for spares to be stocked. There is change being made from ROHS1 to ROHS2 and its hard for us to discern if audio optocouplers are or are not to be given new exemption with ROHS2. On one hand they are non exempt in ROHS1 , but ROHS2 may exempt them again, this should become clearer in August 2014.

In late June we made available our stand alone kit to suit this circumstance, so if you wanted to put one of our kits together you could still do so with lots of help with matching from us which we know is not too popular :eyebrows:. We can still supply as distributors of these parts per the two letters we obtained, one from the National Measurements Office and the other from the EU, but we will abide by the ROHS 2 directive if it is worded as audio optocouplers as non exempt.

Alternative parts
We have put in order for 62 of the Fairchild H11F1M , which is a photo fet optocoupler, its a strange part as it needs lots of resistance prior to it, but it may suit our control board very well, so these will be in and being tested late next week. They will have to equal or exceed ( if thats possible :) ) audio performance we presently get from the NSL32SR2s

We would like forum members to start using our website http://www.stereocoffee.com that links through to Paypal via shoplocket, as maintaining store costs elsewhere has been very expensive for us.

Cheers / Chris